Various fields of use require the use of sterilized polyolefin-based clothing, equipment and tools. For example, it is well known that the operating environments of medical personnel, dental personnel, chemical research personnel, biotech personnel, and other like areas of use all require the use polyolefin-based workwear products that have been sterilized prior to use.
In the past, ethylene oxide has been used to sterilize polyolefin-based products such as medical fabrics that are used as surgical gowns and drapes. However, the potentially hazardous nature and high cost of ethylene oxide sterilization have caused the medical community to consider different sterilization methods. One effective method of sterilization has been the use of gamma irradiation.
Although sterilization by gamma irradiation of polyolefin-based products and equipment has been successful, there remain at least two very undesirable side effects caused by the irradiation process. The first undesirable side effect has been a resulting odor that is so extreme that it renders the gamma irradiated polyolefin-based product undesirable for many uses. The second undesirable side effect has been a noticeably decreased strength of the irradiated polyolefin products. In fact, the irradiation process has been known to decrease a polyolefin-based product's tear strength by as much as 65% of its non-irradiated tear strength.
It has been shown that the cause for the undesirable odor and the loss in fabric strength is a free radical process that occurs when the polyolefins of the product are exposed to gamma radiation in the presence of oxygen. In polyolefin-based products, this process essentially breaks chemical bonds that hold a polyolefin chain together and creates free radicals. This breaking of the polyolefin backbone causes the polyolefin to lose strength proportional to the radiation dosage. The formed radicals are able to recombine with the oxygen in the air, producing short chain acids, oxygenated compounds, such as that become trapped in the product. Butyric acid, one of the acids formed, is a primary suspect in causing the odor.
In efforts to combat these two undesirable side effects, others have tried various processes. For example, U.S. Pat. No. 3,194,668, to Schein and Liberte teaches a process for preparing radiation-stabilized polyethylene products that adds an amount of 2, 2'-methylene-bis-(4-ethyl-6-t-butyl phenyl) to the polyethylene prior to its being sterilized. U.S. Pat. No. 4,501,789 to Burch teaches the pretreatment of polypropylene products with rosin esters, anti-oxidants or prodegradants to reduce the odor caused by the gamma-irradiation of polypropylene products. Further, U.S. Pat. Nos. 4,501,789 and 4,617,230 to Shah, et al. teach the sterilization treatment of polyolefin-based latex non-woven fabrics with an odor inhibition agent selected from amine-type antioxidants and hindered phenols.
Although the above-described patents have taught methods that marginally reduce the odor associated with the gamma irradiation of polyolefin-based products, none has adequately reduced the odor or minimized the reduction in tear strength resulting from the irradiation treatment. A need therefore exists for a method for minimizing or eliminating the odor that is associated with the gamma irradiation of polyolefin-based products. A need further exists for a method that not only reduces the odor, but also minimizes any decrease in the strength of the polyolefin product that is due to the gamma irradiation. Ideally, this need will be satisfied by a method that not only minimizes the polyolefin strength loss, but in fact, actually increases the strength of the post-irradiated polyolefin product.
It is therefore an object of the invention to provide a method for reducing both the odor and the polyolefin strength loss associated with the gamma irradiation process.